The application of transgenic and chimeric and approaches represent a major activity of this program. The Transgenic Core provides the scientific staff, mouse breeding colonies, and specialized equipment needed to generate transgenic mice as well as produce chimeric mice for the program's investigators. The services offered include generation of transgenic mice, production of embryonic stem cell chimeras, ovary transplantation, freezing of 8-cell embryos for preservation of mouse strains, embryo transfer to reconstitute mice contaminated with pathogens, maintenance of mouse lines, collection of embryos, and testing of ES cell lines for germ line transmission.